Give every workspace a default team with access to all topics

[rowanseymour]

Where am going with this...

• Every workspace will have a system team called All Topics (???).
• It's marked as being the default (like how General is the default topic) and it's marked as having access to all topics.
• Every agent always belongs to a team (defaults to the default team).
• If you delete a team its agents are re-assigned to the default team.
• If any agent accepts an invitation and the team has been deleted they are added to the default team.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (3d98249) to head (a647703).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #5576   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          547       548    +1     
  Lines        25643     25656   +13     
=========================================
+ Hits         25643     25656   +13     

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